Warming‐induced functional shifts in the decomposer community interact with plant community compositional shifts to impact litter decomposition

Climate warming is altering plant and soil microbial communities, with important implications for ecosystem processes like litter decomposition. As warming alters plant community composition, the quality of litter will change. Further, shifts in microbial community activity and/or composition will alter microbial function. However, it is not yet completely understood how these shifts will interact to drive decomposition. We explored how changes in plant and microbial communities interact to influence litter decomposition using a 15‐year‐old grassland warming experiment. Previous studies within this system have shown that warming shifted the microbial community in ways that accelerate litter decomposition while simultaneously shifting the plant community in ways that may slow decomposition. Specifically, warming increased abundance ofSorghastrum nutans, while decreasing abundance of the previously dominantSchizachyrium scoparium. Using a series of lab‐based microcosm experiments, we examined the rate at which eight common grasses and, separately, varying abundances ofS. nutansandS. scopariumdecomposed. Using litter and soil from the warming experiment, we then incubated soils from warmed or control plots with different abundances ofS. nutansandS. scopariumin a reciprocal design. We foundS. nutansto be the slowest‐decomposing grass in our system. Further, decomposition slowed asS. nutansincreased andS. scopariumdecreased. When examining the interaction of plant and microbial communities, decomposition was generally greater early in our experiment as the relative abundance ofS. scopariumincreased. However, soil microbial community origin and litter composition interacted significantly. Specifically, decomposition increased with greater relative abundance ofS. scopariumon soils derived from control plots, while litter composition did not shape rates of decomposition on soils from warmed plots. The influence of litter species on decomposition waned in the later stages of the experiment when decomposition was driven by microbial community origin. These results suggest that warming‐induced changes in microbial community function may interact with changes in plant litter composition to mitigate the impacts of warming on rates of decomposition. This emphasizes the importance of considering concurrent warming‐induced changes in both plant and microbial communities on ecosystem processes like decomposition. Read the free Plain Language Summary for this article on the Journal blog.